This invention relates to semiconductor wafer processing and to cleaning the surfaces of semiconductor wafers.
Semiconductor wafers are used to manufacture integrated circuits. During the manufacturing process, wafers are put through chemical mechanical polishing (CMP). In the CMP process, the wafers are mounted on rotating holders and lowered onto a pad surface rotating in the opposite direction. A slurry of silica suspended in a mild etchant, such as potassium or ammonium hydroxide, is applied to the polishing pad. The alkaline slurry chemically grows a thin layer of silicon dioxide on the wafer surface. The buffing action of the pad mechanically removes the oxide in a continuous action. High points on the wafer surface are removed until an extremely flat surface is achieved.
After the CMP process is completed, the wafer surfaces are covered in particles, referred to as a slurry residue. Some of the slurry residue may be distributed across the top and bottom surfaces of the wafer. To remove the particles and prevent the slurry redistribution, the surfaces of a wafer are cleaned. If the slurry residue is not cleaned off the wafer surfaces, there could be a loss in die yield and/or device performance.
Different post-CMP cleaning methods have been used. These include cleaning the wafers in wet stations, or scrubbing wafers with brushes and deionized water or a combination of deionized water and chemicals such as ammonia and citric acid.
Scrubbers are automated devices that are used to remove slurry residue, contaminants and other particles from the surfaces of a semiconductor wafer. Scrubbers typically include one or more rotating cylindrical brushes that contact and brush the slurry residue, particles and other contaminants from a wafer surface. Double sided scrubbers simultaneously scrub the top and bottom surfaces of a semiconductor wafer with two rotating cylindrical brushes. In a typical scrubber, each semiconductor wafer lies flat on a conveyor mechanism which moves the wafer into and between the brushes. When the wafer is being scrubbed, the conveyor mechanism, rollers and brushes support and hold the wafer horizontally. The wafer itself also may be rotated while one or both surfaces are scrubbed by the brushes. One or more rollers may engage the edge of the semiconductor wafer to rotate the wafer.
In scrubbers, the brushes that contact and clean the top and bottom surfaces of the wafer are cylindrical bodies with nubs or bristles extending and protruding outwardly from the external surface of the body. The bristles may be made from a variety of materials including poly vinyl alcohol, nylon, or polyurethane, for example. Bristles or nubs may be mounted in holes in the external surface of the body.
The bristles or nubs on brushes for cleaning surfaces of semiconductor wafers can scratch the surfaces of wafers and/or damage the surfaces on the wafers, especially near the center of the wafers. For example, scratches can irretrievably damage sensitive patterned surfaces of semiconductor wafers. Brushes in scrubbers also may not effectively remove all the slurry residue, particles and/or contaminants from the wafer surface. A wafer having slurry residue, particles or other contaminants remaining on one or both of its surfaces could result in reduced die yield from the wafer.
A brush for a scrubber is needed that will not scratch the wafer surface and will better remove slurry residue, particles and other contaminants from both surfaces. There also is a need to reduce the time for a brush in a wafer scrubber to effectively clean the slurry residue, particles and contaminants from the top and bottom surfaces of each wafer, to increase the volume and throughput of scrubbers.